The invention relates to a surrounding circuit for the coaxial Ethernet/Cheapernet Type local area network transceiver (FIG. 3) especially which is applied to improve the rising time and falling time of the signal and eliminate the Common Mode Noise, and that can have the effect of isolation.
In the situation of high-speed transmission, the rising time and falling time of the signal is very short and many high-frequency components inside can cause an Federal Communications Commission (FCC) failure. In addition, the network signal must be isolated from the local transceiving surrounding apparatus to achieve the objectives of eliminating the Common Mode Noise and preventing the static discharge.
Moreover, in the signal of the Ethernet/Cheapernet Type coaxial local area network, besides that of the high-frequency signal the low-frequency components must be monitored by the transceiver as well, to detect the collision.
To sum up, the surrounding circuit must achieve the following seven missions.
(1) Transmitting the network signal with good waveform. (controlled rising time and falling time) PA1 (2) Electrical isolation or the transmitting and receiving circuits from the network without interfering with the input and output of the normal signal. PA1 (3) Enabling the high-frequency signal to be monitored by the transceiving circuit. PA1 (4) Enabling the low-frequency collision signal to be monitored by the transceiving circuit as well. PA1 (5) Maintaining the high input impedance without affecting the network operation. PA1 (6) Requiring the high output impedance (similar to current source) to show an additive effect. When two transmitters transmit simultaneously, the signal must add up to indicate the Collision. PA1 (7) The transceiving surrounding apparatus can operate normally without additional power supply or a DC/DC converter.
In view of this, the inventor considered providing a kind of circuit which not only enables the required output signal waveform similar to the sine wave, but also eliminate the Common Mode Noise and has the effect of isolation. Meanwhile, it can maintain sufficient high input/output impedance, and detect a collision condition.